Over the past ten years there has been an increasing interest in, and use of, perforated biocompatible metallic strips and panels as a means for rigid internal fixation of fractures in trauma surgery, as a plate material for bone part immobilization and stabilization, and as bone graft support material in orthognathic and reconstructive surgery. Of particular interest has been the use of perforated strips and panels of titanium as an unequaled implant material in use clinically for over 30 years with no documented cases of allergic reactions or rejections by interfacing tissue. Pure titanium is the material of choice in craniofacial reconstructive surgery when non-removal of the implant is indicated. As an implant material, pure titanium is preferred because its low density (weight) and elastic modulus (stiffness) are approximately one-half that of stainless steel or cobalt-chromium alloys and the material is corrosion resistant and pliable. Bone plates made from perforated titanium strips and perforated titanium panels can be cut to appropriate configuration and contoured at the time of surgery and, when affixed to bone fragments or bone sections with bone screws, provide solid, stable fixation means during trauma surgery and planned reconstructive surgery.
One preferred form of perforated titanium strips and panels (titanium mesh) includes rows of substantially square perforations which are formed in titanium sheet material by mechanical means (stamping and machining), by electrical arc cutting, and by milling techniques which preserve the stress free condition of the sheet material. The use of titanium mesh with square holes for internal fixation of bone fractures and for reconstructive surgery provides the surgeon with an implantable plate material which can be easily cut to desired contour and shaped or bent to conform to bone fracture and bone reconstruction sites without inducing mechanical stresses into the material because the formability of such mesh is equal along each of the mesh legs which define each of the square holes. Also, as a perforated sheet material the mesh plate structure provides the surgeon with a multiplicity of ready-made holes through which bone screws can be seated and applied to fasten the plate structure to bone fragments and bone sections. Bending of the perforated sheet material does not distort the square holes to the extent that bone screws can not be applied. This is not the case with mesh implant structures wherein the perforations are round holes.
Implantable square-hole titanium mesh structures of the type described above have been fabricated from sheet titanium having a thickness of 1 mm or less. Titanium mesh strips may be obtained with 1 to 4 lines of square perforations in lengths up to 5 inches or more with the perforations arranged uniformly in 30 or more rows. Mesh panels may be obtained with 15 or more lines of square perforations arranged uniformly in 30 more rows. A preferred form of square-hole titanium mesh is that mesh provided with the holes chamfered for receiving the hemispherical underside of low profile bone screws thereby reducing the possibility of screw-head protrusion with respect to the affixation of mesh strips and plates at or near body surfaces.
Another type of implantable perforated titanium strip and panel structure is formed from a thin sheet of titanium as a mesh-like grid of bars or legs forming various geometric open grid shapes. The bars or legs are connected to one-another in land areas or affixation sections of the grid which each include a screw hole through which a bone screw may be applied to affix the grid to bone and/or bone parts. Thus, the grid-type strips and panels may include connected bars or legs which define square, rectangular, triangular, trapezoidal and other plane geometric configurations (or combinations thereof) of open spaces in a single row or multiple rows. The grid bars or legs at each geometric corner of the grid structure (as few as two and as many as six or more legs) are affixed to a land area or affixation section which includes a screw hole. Implantable grid structures of the type described above have been fabricated from titanium sheet material having a thickness of as little as 0.5 mm with the grid legs being as small as 5 mm in length and having a width of 1 mm and the land areas or affixation sections including a screw hole for a screw having a thread diameter of as little as 1 mm. The grid screw holes are chamfered for receiving the hemispherical underside of low profile bone screws. Such grid implant structures are particularly designed to cover with grid structure material per se less than 50% of the bone area to which the structure is applied. In other words, the grid structure is comprised of at least 50% open area.
While the implantable, perforated titanium mesh and grid structures described above are entirely suitable for a multitude of orthognathic and reconstructive surgery procedures and situations, they are not, in and of themselves, always applicable to surgical bone repair and bone regeneration situations wherein it is desirable or necessary to prevent the invasion at the surgical site of body cells which are competitive to or harmful to bone and/or soft tissue repair and regeneration. Further, although such mesh and grid structures are highly desirable in their ability to be bent, contoured and shaped to conform to bone fracture and reconstruction sites, they do not provide means per se to guide tissue regeneration and promote the enlargement of bone tissue.
It is a principal object of the present invention to provide unique perforated metallic implant structures for the internal fixation of bone fractures and for use in orthognathic and reconstructive surgery which have incorporated therewith microporous membrane material which selectively admits biological nutrients to the tissues at the surgical site fixed and protected by the implant structure and which excludes unwanted cells which are harmful and/or competitive to the tissue healing process.
It is a further object of the invention to provide unique mesh- and grid-type composite metallic implant plate structures which are pliable and contourable for use in orthognathic and reconstructive surgery and the correction of cranial defects and which have incorporated therewith a layer of microporous membrane material which selectively prevents the invasion of harmful and/or competitive tissue cells at the surgical site fixed and protected by the-implant structure.
It is a still further object of the invention to provide unique biocompatible mesh- and grid-type composite metallic implant plates which are pliable, shapable and contourable, for use in orthognathic and reconstructive surgery, which have incorporated therewith one or more layers of microporous membrane material which selectively admits biological nutrients to tissues at the surgical Site fixed and protected by such plates and which excludes unwanted cells.
It is yet another object of the invention to provide unique biocompatible implant structures, for the surgical internal fixation and protection of bone fractures and for the surgical correction of cranial defects, which are comprised of composites of one or more layers of mesh- or grid-type metallic plates and one or more layers of microporous membrane material which selectively admit desired biological nutrients to the surgical fixation and correction sites and which exclude from such sites unwanted cells which are harmful and/or competitive to the tissue healing process.
It is still another object of the invention to provide unique biocompatible composite implant structures comprised of pliable and contourable mesh- and grid-type perforated metallic plates in sandwich combination with one or more layers of microporous membrane material for use in the guided regeneration and enlargement of bone tissue at surgical sites that have involved orthognathic and reconstructive surgery and the correction of cranial defects.
It is another object of the invention to provide unique biocompatible composite implant structures comprised of pliable and contourable mesh- and grid-type perforated metallic sheet material in sandwich combination with one or more layers of microporous membrane material for tented placement over a bone defect, with attachment thereof to bone about the periphery of the defect, to provide secluded and protected space for the guided regeneration of bone tissue within the defect and for the exclusion of competing cells from the defect area.
Other objects and advantages of the invention will be apparent from the following summary and detailed description of the unique composite implant structures of the invention taken together with the accompanying drawing figures.